Methods of fabricating interferometric modulators by selectively removing a material

ABSTRACT

Methods for making MEMS devices such as interferometric modulators involve selectively removing a sacrificial portion of a material to form an internal cavity, leaving behind a remaining portion of the material to form a post structure. The material may be blanket deposited and selectively altered to define sacrificial portions that are selectively removable relative to the remaining portions. Alternatively, a material layer can be laterally recessed away from openings in a covering layer. These methods may be used to make unreleased and released interferometric modulators.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Patent Application Ser. No.60/613,401, filed Sep. 27, 2004 which is hereby incorporated byreference in its entirety.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS).

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. An interferometricmodulator may comprise a pair of conductive plates, one or both of whichmay be transparent and/or reflective in whole or part and capable ofrelative motion upon application of an appropriate electrical signal.One plate may comprise a stationary layer deposited on a substrate, theother plate may comprise a metallic membrane separated from thestationary layer by a gap. Such devices have a wide range ofapplications, and it would be beneficial in the art to utilize and/ormodify the characteristics of these types of devices so that theirfeatures can be exploited in improving existing products and creatingnew products that have not yet been developed.

SUMMARY

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Preferred Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One aspect provides a method for making an interferometric modulatorthat includes depositing a material over a first mirror layer; forming asecond mirror layer over the material; and selectively removing asacrificial portion of the material to thereby form a cavity and a poststructure of the interferometric modulator. The post structure includesa remaining portion of the material. In some embodiments, the materialis a material that can be selectively altered to render it easier ormore difficult to remove. For example, the material may be a radiationsensitive polymer such as a photoresist. The formation of the cavity andpost may be facilitated, in the case of a radiation sensitive polymer,by irradiating the polymer in such a way as to make the sacrificialportion selectively removable relative to the remaining portion that isincluded in the post. In other embodiments, the material is notnecessarily selectively altered to make it easier or more difficult toremove, and the selective removal of the sacrificial portion isaccomplished by selective etching techniques relative to othersurrounding materials as the material is laterally recessed away fromcarefully positioned openings in an overlying cover layer.

Another aspect provides an unreleased MEMS substrate that includes amaterial, the MEMS substrate being configured so that a sacrificialportion of the material is removable to form a cavity and so that aremaining portion of the material forms a post structure of aninterferometric modulator upon removal of the sacrificial portion. Thematerial may be a material that can be selectively altered to renderportions of it selectively removable to other portions, or may be amaterial that is removable by selective etching techniques relative toother surrounding materials.

Another aspect provides a method for making an interferometricmodulator. The interferometric modulator includes at least a firstmirror, a second mirror separated from the first mirror by a cavity, anda post structure positioned at a side of the cavity and configured tosupport the second mirror spaced from the first mirror. The method formaking this interferometric modulator includes providing a substrate,the substrate having a first area configured to underlie the firstmirror and a second area configured to underlie the post structure, thendepositing a first mirror layer over at least the first area. The methodfurther includes depositing a material over the first area and thesecond area and selectively altering the material over the first area,the material over the second area, or both. The method further includesdepositing a second mirror layer over at least the first area. Thematerial over the first area is selected to be removable so that, uponremoval of a sacrificial portion, a cavity and a post structure of theinterferometric modulator are formed, where the post structure includesthe material over the second area that remains after removal of thesacrificial portion. The material may be a material that can beselectively altered to render it easier or more difficult to remove, ormay be a material that is removable by selective etching techniques.

Another aspect provides a method for making an interferometric modulatorthat includes depositing a material over a first mirror layer anddepositing a second layer over the material. The second layer includesan opening formed through the second layer and configured to expose thematerial. The method further includes flowing an etchant through theopening and etching the material for a period of time that is effectiveto remove a sacrificial portion of the material to thereby form a cavityand a post structure of the interferometric modulator, the poststructure comprising a remaining portion of the material. The etchingmay include laterally recessing the material away from the opening. Thepost structure formed by the method may have a re-entrant profile.

Another aspect provides an unreleased MEMS substrate that includes anunderlying material and an overlying layer. The overlying layer isconfigured so that a sacrificial portion of the material is removable toform a cavity. The overlying layer is also configured so that aremaining portion of the material forms a post structure of aninterferometric modulator upon removal of the sacrificial portion.

Another aspect provides a method for making an interferometricmodulator. The interferometric modulator includes at least a firstmirror, a second mirror separated from the first mirror by a cavity, anda post structure positioned at a side of the cavity and configured tosupport the second mirror spaced from the first mirror. The method formaking the interferometric modulator includes providing a substrate thathas a first area configured to underlie the first mirror and a secondarea configured to underlie the post structure, and depositing a firstmirror layer over at least the first area. The method further includesdepositing a material over the first area and over the second area, anddepositing a second mirror layer over at least the material over thefirst area. The method further includes forming a plurality of openingsconfigured to facilitate flow of an etchant to the material over thefirst area. The material over the first area is removable by the etchantto thereby form the cavity and the post structure, where the poststructure comprises the material over the second area.

Another aspect provides an interferometric modulator that includes apost structure that has a re-entrant profile. For example, the poststructure may have a generally concave cross-section or a generallyconvex cross-section.

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a released position and amovable reflective layer of a second interferometric modulator is in anactuated position.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIG. 6A is a cross section of the device of FIG. 1.

FIG. 6B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 6C is a cross section of another alternative embodiment of aninterferometric modulator.

FIGS. 7-9 show cross sectional views that schematically illustrateaspects of a process flow for the fabrication of an interferometricmodulator.

FIGS. 10-11 show cross sectional views of an embodiment thatschematically illustrate aspects of a process flow for the fabricationof an interferometric modulator.

FIG. 12 show cross sectional views of an embodiment that schematicallyillustrate aspects of a process flow for the fabrication of aninterferometric modulator.

FIGS. 13-15 show cross sectional views of an embodiment thatschematically illustrate aspects of a process flow for the fabricationof an interferometric modulator.

FIG. 16 shows a top view photomicrograph of an embodiment depictingradial etching by a XeF₂ etchant flowing through a via of aninterferometric modulator substrate.

FIGS. 17A-17E show top view photomicrographs of an embodiment depictingthe progressive etching of a interferometric modulator substrate by aXeF₂ etchant flowing through an array of vias.

FIGS. 18A-18C show top view photomicrographs of an embodiment depictingthe progressive etching of an interferometric modulator substrate by aXeF₂ etchant flowing through an array of horizontal and vertical vias.

FIG. 19 shows cross sectional views of an embodiment that schematicallyillustrate aspects of a process flow for the fabrication of aninterferometric modulator in which the upper mirror layer is suspendedfrom a deformable or mechanical layer.

FIGS. 20A-20B show cross sectional views of an embodiment thatschematically illustrate aspects of a process flow for the fabricationof an interferometric modulator in which the upper mirror layer issuspended from a deformable or mechanical layer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments are directed to methods for making interferometricmodulators in which the internal cavities and posts are both formed froma blanket layer by selectively removing a material, leaving behind theremaining material to form post structures. These methods may be used tomake unreleased and released interferometric modulators. For example, anunreleased interferometric modulator substrate may be formed bydepositing a first mirror layer, depositing a photosensitive polymerover the first mirror layer and over an adjacent area that will underliea post structure in the resulting interferometric modulator, and thendepositing a second mirror layer over the photosensitive polymer. Thephotosensitive polymer is irradiated to render a sacrificial portion ofthe photosensitive polymer that is between the first mirror layer andthe second mirror layer selectively removable, thereby forming a cavity.The portion of the photosensitive polymer that is over the area that isadjacent to the first mirror layer remains behind to form a poststructure after removal of the sacrificial portion. In anotherembodiment, the material between the mirror layers need not be aphotosensitive polymer. For example, the material may be a blanketmolybdenum layer and the overlying second mirror layer may be providedwith vias that are positioned to allow a etchant (such as XeF₂) toselectively etch the molybdenum relative to the mirror layers. Themolybdenum is thus recessed laterally under the second mirror layer, butonly a sacrificial portion of the molybdenum is removed, leaving aremaining part of the molybdenum behind to form posts.

An embodiment provides a method for making an interferometric modulatorcomprising depositing a photosensitive polymer onto a substrate andselectively irradiating the photosensitive polymer to form a sacrificiallayer and a post structure. For example, the photosensitive polymer maybe selectively crosslinked by irradiation to form a post structure inthe selectively irradiated areas and a sacrificial layer in thenon-irradiated areas. The non-irradiated sacrificial portions arereadily susceptible to removal by dissolution, e.g., by washing withcommercially available resist stripping solutions that do not remove theirradiated portions. As another example, the photosensitive polymer maybe selectively degraded by irradiation to form a sacrificial layer inthe selectively irradiated area and a post structure in non-irradiatedareas. In another embodiment, the method is continued by selectivelyetching the sacrificial layer (e.g., using a solvent that preferentiallydissolves the sacrificial layer, leaving the post structure).

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout.

As will be apparent from the following description, the structuredescribed herein may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the structures and methods may be implemented in orassociated with a variety of electronic devices such as, but not limitedto, mobile telephones, wireless devices, personal data assistants(PDAs), hand-held or portable computers, GPS receivers/navigators,cameras, MP3 players, camcorders, game consoles, wrist watches, clocks,calculators, television monitors, flat panel displays, computermonitors, auto displays (e.g., odometer display, etc.), cockpit controlsand/or displays, display of camera views (e.g., display of a rear viewcamera in a vehicle), electronic photographs, electronic billboards orsigns, projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as thereleased or relaxed state, the movable layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, the movable layer is positioned more closelyadjacent to the partially reflective layer. Incident light that reflectsfrom the two layers interferes constructively or destructively dependingon the position of the movable reflective layer, producing either anoverall reflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable and highly reflective layer 14 ais illustrated in a relaxed position at a predetermined distance from afixed partially reflective layer 16 a. In the interferometric modulator12 b on the right, the movable highly reflective layer 14 b isillustrated in an actuated position adjacent to the fixed partiallyreflective layer 16 b.

The fixed layers 16 a, 16 b are electrically conductive, partiallytransparent and partially reflective, and may be fabricated, forexample, by depositing one or more layers each of chromium andindium-tin-oxide onto a transparent substrate 20. The layers arepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. The movable layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes 16 a, 16 b) deposited on top ofposts 18 and an intervening sacrificial material deposited between theposts 18. When the sacrificial material is etched away, the deformablemetal layers are separated from the fixed metal layers by a defined gap19. A highly conductive and reflective material such as aluminum may beused for the deformable layers, and these strips may form columnelectrodes in a display device.

With no applied voltage, the cavity 19 remains between the layers 14 a,16 a and the deformable layer is in a mechanically relaxed state asillustrated by the pixel 12 a in FIG. 1. However, when a potentialdifference is applied to a selected row and column, the capacitor formedat the intersection of the row and column electrodes at thecorresponding pixel becomes charged, and electrostatic forces pull theelectrodes together. If the voltage is high enough, the movable layer isdeformed and is forced against the fixed layer (a dielectric materialwhich is not illustrated in this Figure may be deposited on the fixedlayer to prevent shorting and control the separation distance) asillustrated by the pixel 12 b on the right in FIG. 1. The behavior isthe same regardless of the polarity of the applied potential difference.In this way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application. FIG. 2is a system block diagram illustrating one embodiment of an electronicdevice that may incorporate aspects of the invention. In the exemplaryembodiment, the electronic device includes a processor 21 which may beany general purpose single- or multi-chip microprocessor such as an ARM,PENTIUM®, PENTIUMII®, PENTIUMBIII®, PENTIUMIV®, PENTIUM® PRO, an 8051, aMIPS®, a POWER PC®, an ALPHA®, or any special purpose microprocessorsuch as a digital signal processor, microcontroller, or a programmablegate array. As is conventional in the art, the processor 21 may beconfigured to execute one or more software modules. In addition toexecuting an operating system, the processor may be configured toexecute one or more software applications, including a web browser, atelephone application, an email program, or any other softwareapplication.

In one embodiment, the processor 21 is also configured to communicatewith an array controller 22. In one embodiment, the array controller 22includes a row driver circuit 24 and a column driver circuit 26 thatprovide signals to a pixel array 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column were set toduring the row 1 pulse. This may be repeated for the entire series ofrows in a sequential fashion to produce the frame. Generally, the framesare refreshed and/or updated with new display data by continuallyrepeating this process at some desired number of frames per second. Awide variety of protocols for driving row and column electrodes of pixelarrays to produce display frames are also well known and may be used inconjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias).

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thepresent invention.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6C illustrate three different embodiments of themoving mirror structure. FIG. 6A is a cross section of the embodiment ofFIG. 1, where a strip of metal material 14 is deposited on orthogonallyextending supports 18. In FIG. 6B, the moveable reflective material 14is attached to supports at the corners only, on tethers 32. In FIG. 6C,the moveable reflective material 14 is suspended from a deformable layer34. This embodiment has benefits because the structural design andmaterials used for the reflective material 14 can be optimized withrespect to the optical properties, and the structural design andmaterials used for the deformable layer 34 can be optimized with respectto desired mechanical properties. The production of various types ofinterferometric devices is described in a variety of publisheddocuments, including, for example, U.S. Application Publication No.2004/0051929. A wide variety of well known techniques may be used toproduce the above described structures involving a series of materialdeposition, patterning, and etching steps.

Interferometric modulators of the general design discussed abovecomprise an interferometric cavity (e.g., cavity 19 in FIGS. 1 and 6)and a post structure (e.g., support 18 in FIGS. 1 and 6), and may befabricated using the techniques disclosed and/or referenced in U.S.Application Publication No. 2004/0051929. FIGS. 7-9 schematicallyillustrate aspects of a fabrication process for an interferometricmodulator in which the post structure is formed by depositing asacrificial layer, forming holes in the sacrificial layer, depositing apolymer in the holes, and later removing the sacrificial layer, leavingthe polymer behind to form the posts. Those skilled in the art willappreciate that the fabrication processes described herein may becarried out using conventional semiconductor manufacturing techniquessuch as photolithography, deposition (e.g., “dry” methods such aschemical vapor deposition (CVD) and wet methods such as spin coating),masking, etching (e.g., dry methods such as plasma etch and wetmethods), etc.

FIG. 7 illustrates the formation of a first mirror layer 315 bydeposition of mirror material 310 on a substrate 305 and subsequentpatterning and etching. FIG. 7 further illustrates deposition of adielectric layer 320 over the first mirror layer 315 and the exposedsubstrate 305. The mirror material is electrically conductive and maycomprise a metal or a semiconductor (such as silicon) doped to have thedesired conductivity. In one embodiment, the first mirror layer 315 is amultilayer structure comprising a transparent conductor (such as indiumtin oxide) and a primary mirror (such as chromium). In anotherembodiment, the first mirror layer 315 is a multilayer structurecomprising a transparent conductor (such as indium tin oxide), adielectric layer (silicon oxide) and a primary mirror. In a number ofembodiments the first mirror layer (e.g., the first mirror layer 315)also functions as an electrode, and thus the terms “electrode,” “mirror”and “mirror layer” may be used interchangeably herein. The dielectriclayer 320 may be silicon oxide.

The fabrication process continues as illustrated in FIG. 8 by depositinga sacrificial layer 405 over the dielectric layer 320 to form astructure 400, masking and etching the sacrificial layer 405 to formholes 410, and depositing a polymer in the holes 410 to form poststructures 415. The sacrificial layer may be a material (such asmolybdenum or silicon) that is capable of being etched by exposure toXeF₂ vapor. The polymer may be a negative photoresist material. A secondmirror layer 505 is then deposited over the post structures 415 and thesacrificial layer 405 as illustrated in FIG. 9. The second mirror layer505 is electrically conductive and may be a metal or a semiconductor(such as silicon) doped to have the desired conductivity. In alternateprocess flows (not shown in FIG. 9), a multi-step process is used tofabricate a second mirror layer that is suspended from a mechanicallayer (e.g., as illustrated in FIG. 6C). For embodiments in which thesecond mirror layer (e.g., the second mirror layer 505) also functionsas an electrode, the terms “electrode,” “mirror” and “mirror layer” maybe used interchangeably. In the illustrated embodiment, the secondmirror layer 505 also has a mechanical function during operation of theresulting interferometric modulator, and thus may be referred to hereinas a “mechanical” or “deformable” layer. In other configurations, themirror layer is suspended from the mechanical or deformable layer, e.g.,the mirror 14 may be suspended from the deformable layer 34 asillustrated in FIG. 6C. The sacrificial layer 405 is then removed by,e.g., etching, to form an interferometric cavity 510 as illustrated inFIG. 9. A molybdenum or silicon sacrificial layer may be removed byexposure to XeF₂ vapor. Those skilled in the art will understand that inthe process flow for fabricating an interferometric modulatorillustrated in FIGS. 7-9, the sacrificial layer and post structure areformed from different materials, e.g., molybdenum (sacrificial layer)and polymer photoresist (post structure), that are deposited atdifferent stages of the fabrication process.

An improved process for fabricating an interferometric modulator has nowbeen developed that involves depositing a layer of material over a firstmirror layer, forming a second mirror layer over the material, and thenselectively removing a sacrificial portion of the layer of material toform a cavity and a post structure. The post structure contains aremaining portion of the material layer that is not removed. In someembodiments, the material that is deposited over the first mirror layer(and then selectively removed to form the cavity and post structure) hassubstantially uniform composition when initially deposited, but isselectively altered during the fabrication process so that thesacrificial portion is easier to remove than the remaining portion thatforms the post structure. Selective removal techniques may be used tofacilitate removing the sacrificial portion. In other embodiments, thematerial has a substantially uniform composition throughout depositionand removal, and selective removal techniques (relative to surroundingmaterials, such as an overlying mechanical layer and underlyingdielectric layer) are applied to remove the sacrificial portion (e.g.,by isotropic lateral recessing), leaving the remaining portion behind toform at least part of the posts. These and other embodiments aredescribed in greater detail below.

In one embodiment, the material has substantially uniform propertieswhen initially deposited, but is selectively altered during thefabrication process so that the sacrificial portion can be selectivelyremoved relative to the remaining portion that forms the post structure.Such an embodiment is illustrated in FIG. 10. The process shown in FIG.10 begins with a structure 600 that includes a substrate 605, a firstmirror layer 610 over the substrate 605, a dielectric layer 615 over thefirst mirror layer 610 and the substrate 605, and a material 620 overthe dielectric layer 615. The structure 600 may be fabricated in thegeneral manner described above with respect to making the structure 400illustrated in FIG. 8, except that the material 620 is a material thatis capable of being selectively altered so that a sacrificial portion isselectively removable relative to the unaltered portion of the material.Photosensitive polymers are non-limiting examples of such materials.Photosensitive polymers include positive photoresists and negativephotoresists. Exposure of a positive resist to radiation (e.g.,ultraviolet light) alters the polymer so that it becomes easier toremove. Exposure of a negative photoresist to radiation (e.g.,ultraviolet light) alters the polymer so that it becomes more difficultto remove. Photosensitive polymers can be selectively irradiated byknown techniques (e.g., by masking) so that one or more portions of thepolymer are easier to remove than one or more other portions. Silicon isanother example of a material that is capable of being selectivelyaltered so that a sacrificial portion is removable. For example, siliconmay be selectively altered by ion implantation with oxygen atoms to formsilicon oxide(s). Various selective removal chemistries are available toselectively etch silicon oxide(s) relative to silicon and vice versa.Other selective removal chemistries are available for the selectiveremoval of other material systems, e.g., doped vs. undoped silicon,doped vs. undoped silicon oxide(s); nitrided or silicided metal vs.metal, etc. Selective alteration may be conducted by masking a basematerial (e.g., silicon) and implanting the appropriate ions (e.g.,implanting oxygen atoms to form silicon oxide(s)) in the unmasked areas.Preferably, the material 620 is a photoresist that can be patternedusing a reticle that blocks light from reaching selected areas of thephotoresist during irradiation. The use of such a reticle may reduce oreliminate masking of the base material. Another advantage ofphotoresists is that they are typically self-planarizing, as they aredeposited by spin-on deposition processes.

In the illustrated embodiment, the material 620 is a photosensitivepolymer. In FIG. 10, the material 620 is selectively irradiated (e.g.,by suitable masking, not shown) to form irradiated portions 625 in theselectively irradiated areas and non-irradiated portions 621 remainingin the non-irradiated areas. In this embodiment, the material 620 is aphotosensitive polymer that undergoes crosslinking upon irradiation(e.g., a negative photoresist). Such photosensitive polymers are wellknown to those skilled in the art. The crosslinking hardens the polymerto form the irradiated portions 625, so that the remainingnon-irradiated portions 621 may be selectively removed during a laterstage of the process as described below. In other arrangements, theresist may contain photo acid generators (PAGs) activated by exposure tolight, rendering the resulting acidic or non-acidic regions selectivelyremovable relative to the other regions.

FIG. 11 shows a second mirror layer 705 is then formed over theirradiated portions 625 and the non-irradiated portions 621 to form anunreleased interferometric modulator substrate 1100. In this embodiment,the second mirror layer 705 has a mechanical function and may bereferred to as a mechanical or deformable layer. The second mirror layer705 may be formed by known deposition techniques, e.g., sputtering orchemical vapor deposition. An optional planarization step may be used toplanarize the upper parts of the irradiated portions 625 and thenon-irradiated portions 621, thus providing a relatively flat surface tounderlie the second mirror layer 705. The second mirror layer 705 iselectrically conductive and may be a metal or a semiconductor (such assilicon) doped to have the desired conductivity. In this embodiment, thesecond mirror layer 705 is an electrode. In alternate process flows (notshown in FIG. 11), a multi-step process is used to fabricate a secondmirror/electrode that is suspended from a mechanical layer (e.g., asillustrated in FIG. 6C).

The non-irradiated portions 621 of the unreleased substrate 1100 arethen removed to form interferometric modulator cavities 710 asillustrated in FIG. 11. The polymer in the irradiated portions 625 hasbeen hardened by crosslinking and thus has a different solubility thatthe non-irradiated portions 621. Crosslinking can be performed usingvarious forms of energy, e.g., UV, ionizing radiation, heat, etc. Thus,for example, by employing the appropriate etch chemistry, thenon-irradiated portions 621 may be selectively removed to form thecavities 710, leaving behind the polymer remaining in the irradiatedportions 625 to form post structures 715. In the illustrated embodiment,selective removal of the non-irradiated portions 621 is accomplished bywashing with a liquid solvent that preferentially dissolves theuncrosslinked polymer in the non-irradiated portions 621. In alternateembodiments, removal may be accomplished by exposure to a plasma orchemical vapor that preferentially etches the non-irradiated portions621.

In another embodiment, illustrated in FIG. 12, a structure 800 is formedin the same general manner as the structure 600 illustrated in FIG. 10,except that a photosensitive polymer 810 is selected that undergoesdegradation upon irradiation (e.g., a positive photoresist) to formirradiated portions 815 in the selectively irradiated areas andnon-irradiated portions 820 remaining in the non-irradiated areas. Suchselective irradiation may be accomplished by e.g., reversing the maskingillustrated in FIG. 10. The fabrication process may then be continued(not shown in FIG. 12) in the general manner described above withrespect to FIG. 11, by depositing a second mirror layer and thenselectively removing the degraded polymer in the irradiated portions 815to form cavities, leaving behind the polymer in the non-irradiatedportions 820 to form post structures.

The processes illustrated in FIGS. 10-12 may also be carried out usingother materials that can be selectively altered so that the alteredportions are selectively removable relative to the unaltered portions.For example, those skilled in the art will understand that silicon canbe selectively altered by oxygen ion implantation through a suitablemask to form silicon oxide(s) in selected area(s). Selective removal ofa sacrificial portion (either the unaltered silicon or the siliconoxide) may then be conducted using a suitable etchant to form a cavityand a post structure in the general manner illustrated in FIGS. 10-12,such that the post structure comprises a remaining portion of thesilicon or silicon oxide(s). Other material systems and selectiveremoval chemistries may also be used as discussed above. Those skilledin the art will also understand that the order of the process stepsillustrated in FIGS. 10-12 may be changed as desired. For example,alteration of the material 620 by selective irradiation to formirradiated portions 625 in the selectively irradiated areas andnon-irradiated portions 621 remaining in the non-irradiated areas asillustrated in FIG. 10 may be conducted prior to forming the secondmirror 705 (as illustrated in FIG. 11). In an alternate embodiment (notillustrated), the material 620 is selectively irradiated after thesecond mirror 705 is formed over the material 620.

In other embodiments, the material deposited over the first mirror layerhas substantially uniform properties throughout deposition and removal,and selective removal techniques are applied to remove sacrificialportions of the material, leaving remaining portions of the materialbehind to form at least part of the posts. The process flow shown inFIGS. 13-14 illustrates such an embodiment. The process begins in FIG.13 with a structure 900 that includes a substrate 902, a first mirrorlayer 904 over the substrate 902, a dielectric layer 906 over the firstmirror layer 904 and the substrate 902, and a material layer 910 overthe dielectric layer 906. The substrate 902 includes a first area 907configured to underlie the first mirror layer 904 and a second area 908configured to underlie a post structure that will be formed as describedbelow.

The structure 900 may be fabricated in the same general manner asdescribed above with respect to making the structure 400 illustrated inFIG. 8. The material 910 is a material that is capable of beingselectively etched relative to other surrounding materials (e.g., thefirst mirror layer 904 and the dielectric layer 906) by exposure to asuitable etchant to remove a sacrificial portion. Molybdenum and siliconare examples of such materials and XeF₂ is an example of a suitableetchant. Those skilled in the art understand that, in this context, theterm “XeF₂ etchant” refers to the gaseous and/or vaporous substanceformed by the sublimation of solid XeF₂, and may include XeF₂, Xe and F₂in gaseous or vapor form. The material 910 is molybdenum in theillustrated embodiment.

The process illustrated in FIG. 13 continues by forming a second mirrorlayer 920 over the molybdenum layer 910 and over the first area 907 toform an unreleased interferometric modulator substrate 911. In theillustrated embodiment, the second mirror layer 920 is also formed overthe second area 908. In a prior intermediate step (not shown), themolybdenum layer 910 was planarized. Such planarization is optional.Those skilled in the art will understand that, in the illustratedembodiment, the second mirror layer 920 also functions as a mechanicallayer and as an electrode in the resulting interferometric modulator,and thus may be referred to as a mechanical layer, deformable layerand/or electrode herein. The process continues by forming vias 925through the second mirror layer 920 to expose the molybdenum layer 910.The vias 925 are formed in the second mirror layer 920 over areas of thestructure 900 in which the creation of optical cavities is desired(e.g., over the first area 907), as explained in greater detail below.The vias 925 may be formed by masking and etching techniques known tothose skilled in the art.

The process continues as illustrated in FIG. 14 by introducing a XeF₂etchant 930 through the vias 925 to isotropically selectively etch themolybdenum layer 910 without substantially etching the dielectric layer906 or the second mirror layer 920. Other selective etchants may also besuitable, depending on the nature of the material 910 and the materialsused to form the dielectric layer 906 and the second mirror layer 920,as well as the exigencies of production. In the illustrated embodiment,etching of the molybdenum layer 910 by the etchant 930 proceeds byforming cavities 935 that laterally undercut the second mirror layer 920and expand in size to form optical cavities 940 over the course of theetching process. The vias 925 are positioned and the etching conditionsare selected so that the etchant 930 removes a sacrificial portion ofthe material layer 910 under the second mirror layer 920 to form theoptical cavities 940 over the first area 907 and over the first mirror904, and so that the remaining portion of the material layer 910 formspost structures 945 that provide support to the second mirror layer 920over the second area 908. Optionally, production may continue to finishmaking a MEMS device such as an interferometric modulator. In theillustrated embodiment, the post structures 945 have a re-entrantprofile that is generally concave in cross-section. Those skilled in theart will understand that the base of the post structures 945 may bewider than the top, as shown. In the illustrated embodiment, the etchantenters through the vias 925 and thus there tends to be more etching nearthe top than the bottom, resulting in post structures 925 that tend tobe wider at the bottom than at the top.

FIG. 15A illustrates another embodiment in which the etchant 930 entersthrough apertures 926 formed through the substrate 902, in which casethere tends to be more etching near the bottom than the top as shown forthe post structure 945 a. In still another embodiment illustrated inFIG. 15B, the etchant 930 enters through both the vias 925 and theapertures 926, in which case there tends to be more etching near the topand the bottom of the post structure than in the middle, as indicated bythe convex cross-section of the post structure 945 b in the illustratedembodiment.

The positioning of the vias 925 and the selection of the etchingconditions to produce cavities and post structures as illustrated inFIGS. 13-15 may be accomplished in various ways. FIG. 16 shows aphotomicrograph of an interferometric modulator substrate (taken fromthe display side) after a controlled amount of a XeF₂ etchant wasintroduced through a via 1505 to etch a molybdenum material. Thephotomicrograph shows that the XeF₂ flows through the via 1505 and thenetches the molybdenum in a generally radial pattern to form a cavity(the cross section is not seen here). This flow pattern may be utilizedto produce an array of interferometric modulator cavities and poststructures as illustrated by the series of photomicrographs shown inFIG. 17.

FIG. 17A shows an array of cavities (including a cavity 1605) havinggenerally circular cross-sections in the molybdenum material of aninterferometric modulator substrate, resulting from the introduction ofa XeF₂ etchant through a corresponding array of vias (e.g., a via 1609).The photomicrograph shown in FIG. 17A was taken about one minute afterthe XeF₂ etchant was introduced through the vias (e.g., the via 1609).FIGS. 17B, 17C, 17D and 17E show photomicrographs of differentinterferometric modulator substrates exposed to the XeF₂ etchant forvarious periods of time. The etched substrates shown in FIGS. 17B-17Eillustrate the effect of introducing the XeF₂ etchant through the vias1609, 1610, and 1615 to thereby etch the molybdenum material for abouttwo, four, six, and eight minutes, respectively. Those skilled in theart will understand that different reference numbers are used to referto the vias in FIGS. 17A, 17D and 17E because different interferometricmodulator substrates (and thus different vias) are illustrated in theseries of representative photomicrographs. The diameter of the vias wasabout 4 microns (um) and the chamber pressure was in the range of about20 mTorr to 2 Torr during the etching processes illustrated in FIG. 17.The series of photomicrographs in FIG. 17 illustrates the manner inwhich the diameters of the cavities would tend to increase as etchingproceeds, from the initial stages in which the edges of the cavities(e.g., cavity edges 1607) are separated from one another to the laterstages, when the cavity edges meet and merge. By stopping the etchingafter the cavity edges merge but prior to complete removal of themolybdenum material, remaining material is left behind to form posts.For example, the diamond-shaped post 1620 in FIG. 17E may be formed byintroducing XeF₂ etchant through the vias 1615 until the correspondingcavities merge.

FIG. 18 illustrates a progression of representative photomicrographsillustrating the formation of interferometric modulator posts 1705 byintroducing a XeF₂ etchant through a series of horizontal and verticalvias 1710. The vias 1710 are openings or channels in the overlying orcovering layer(s), exposing the underlying molybdenum material. In FIG.18A, the interferometric modulator substrate was exposed to XeF₂ vaporfor about 30 seconds. In FIG. 18B, the exposure to XeF₂ was for about 45seconds, and in FIG. 18C, the exposure to XeF₂ was for about one minute.The etching rate may be adjusted as desired by controlling the chamberpressure and/or introducing the XeF₂ gas to the chamber in admixturewith other gas(es), e.g., in admixture with a carrier gas such asnitrogen, helium, xenon, and/or argon. Those skilled in the art willunderstand that apertures (including arrays of apertures) in theoverlying layer and/or the substrate are preferably configured tofacilitate both etching of the material layer to form the cavity andpost structure, and operation of the resulting MEMS device. Thus, forexample, it is preferred that apertures in the mirror layer of aninterferometric modulator be configured to minimize any negative impacton the functioning of the mirror layer. Routine experimentation may beused to identify optimum aperture configurations and etching conditions.

Those skilled in the art will understand that the process embodimentsillustrated in FIGS. 13-18 may also be practiced using materials thatcan be selectively altered so that the altered portions are renderedselectively more or less removable relative to the unaltered portions.For example, the unreleased interferometric modulator substrate 1100illustrated in FIG. 11 may be used in place of the unreleasedinterferometric modulator substrate 911 illustrated in FIG. 13. In sucha case, the vias 925 formed through the second mirror layer 920 toexpose the molybdenum layer 910 (as illustrated in FIG. 13) wouldinstead be formed through the second mirror layer 705 to expose thenon-irradiated portions 621 of unreleased interferometric modulatorsubstrate 1100. Removal of the non-irradiated portions 621 could then beconducted in the same general manner as illustrated in FIG. 14 anddescribed above, with the added advantage of a wider processing window(e.g., because less risk of over-etching of irradiated portions 625after removal of non-irradiated portions 621).

The processes described herein are also applicable to the manufacture ofunreleased and released interferometric modulators of the general typeillustrated in FIG. 6C, in which a second mirror layer (the moveablereflective material 14) is suspended from a deformable layer 34.Interferometric modulators of the general type illustrated in FIG. 6Cmay be fabricated as described in U.S. Patent Publication No.2004/0051929 A1. Aspects of a method for fabricating interferometricmodulators of the general type illustrated in FIG. 6C are illustrated bythe schematic cross-sectional views shown in FIG. 19. An unreleasedinterferometric modulator 1800 includes a substrate 1805, a first mirrorlayer 1810 over the substrate 1805, a dielectric layer 1815 over thefirst mirror layer 1810, and a first portion of sacrificial material1835 over the dielectric layer 1815. A second mirror layer 1820 isformed over a portion of the sacrificial material 1835, and a secondportion of sacrificial material 1845 is formed over the second mirrorlayer 1820. The second mirror layer 1820 is attached to a deformable ormechanical layer 1825 formed over the second portion of sacrificialmaterial 1845. Posts 1830 are formed through vias in the first andsecond portions of the sacrificial material 1835, 1845. The posts 1830are configured to support the mechanical layer 1825 after thesacrificial material 1835, 1845 is removed. Exposure of the sacrificialmaterial 1835, 1845 to an etchant results in the formation of a releasedinterferometric modulator 1850 having interferometric cavities 1855 asillustrated in FIG. 19. After such removal, the second mirror layer 1820is suspended from the deformable or mechanical layer 1825.

Using variants of the process described above and illustrated in FIGS.7-9, interferometric modulators of the general type illustrated in FIG.19 may be fabricated by methods known to those skilled in the art byusing different materials to form the posts 1830 and the sacrificialmaterial 1835, 1845. In an embodiment, it has now been found thatinterferometric modulators of the general type illustrated in FIG. 19may also be fabricated by depositing a material over a first mirrorlayer; forming a second mirror layer over the material; and selectivelyremoving a sacrificial portion of the material to thereby form a cavityand a post structure of the interferometric modulator, the poststructure comprising a remaining portion of the material. Aspects ofsuch an embodiment are illustrated in FIG. 20.

FIG. 20B shows a cross-sectional schematic view of an unreleasedinterferometric modulator substrate 1900 that includes a substrate 1905,a first mirror layer 1910 over the substrate 1905, a dielectric layer1915 over the first mirror layer 1910, and a lower portion of a material1935 over the dielectric layer 1915. A second mirror layer 1920 isformed over the lower portion of the material 1935, and an upper portionof the material 1945 is formed over the second mirror layer 1920. Thesecond mirror layer 1920 is attached to a deformable or mechanical layer1925 formed over the upper portion of material 1945. The upper and lowerportions of the material 1935, 1945 are also formed over areas 1930 ofthe substrate 1905 configured to underlie support posts which will beformed as described below. In the illustrated embodiment, the upper andlower portions of the material 1935, 1945 comprise a negativephotoresist that is altered when exposed to radiation (e.g., ultravioletlight). Aspects of a process for making the unreleased interferometricmodulator substrate 1900 are illustrated in FIG. 20A and include formingthe first mirror layer 1910 and dielectric layer 1915 on the substrate1905, depositing a photoresist layer 1918 over the dielectric layer1915, then forming the second mirror layer 1920 over the photoresistlayer 1918 by patterning and etching. The photoresist layer 1918includes the lower portion of the material 1935 under the second mirrorlayer 1920. A photoresist layer 1919 is then deposited over thephotoresist layer 1918 and over the second mirror layer 1920. Thephotoresist layer 1919 includes the upper portion of the material 1945over the second mirror layer 1920. The photoresist layer 1919 is thenmasked and etched to form vias.

As illustrated in FIG. 20B, the unreleased interferometric modulatorsubstrate 1900 is suitably exposed to ultraviolet radiation through areticle and the upper and lower portions of the material 1935, 1945 thatare over the areas 1930 of the substrate 1905 are altered by exposure toultraviolet light. The upper and lower portions of the material 1935,1945 that are not over the areas 1930 of the substrate 1905 (includingthe lower portion of the material 1935 underlying the second mirrorlayer 1920 and the upper portion of the material 1945 overlying thesecond mirror layer 1920) are not exposed to ultraviolet light and thusform sacrificial material. The mechanical layer 1925 is then formed andattached to the second mirror layer 1920. The sacrificial material isthen removed (e.g., by washing with a suitable solvent) to form cavities1955. The altered upper and lower portions of the material 1935, 1945over the areas 1930 remain and form posts 1960, resulting in a releasedinterferometric modulator 1950.

Those skilled in the art will understand that interferometric modulatorsof the general type illustrated in FIG. 6C may also be fabricated usingvariants of the method illustrated in FIG. 20. For example, in anembodiment, the material 1935, 1945 may comprise a positive photoresist,in which case the pattern of exposure to irradiation through the reticleis reversed in a manner similar to that described above for theembodiment illustrated in FIG. 12. In another exemplary embodiment, thematerial 1935, 1945 comprises silicon, and is selectively altered byoxygen ion implantation to form a silicon oxide in a manner similar tothat described above for the embodiment illustrated in FIG. 10. Thus,for example, the silicon may be removed to form a cavity, e.g., byselectively etching against the silicon oxide, leaving the remainingsilicon oxide to form a post. In another exemplary embodiment, selectiveetching techniques similar to those described above for the embodimentsillustrated in FIGS. 13-18 are applied to the material 1935, 1945,including optional alteration of the material prior to such selectiveetching to make the sacrificial portions selectively etchable relativeto the portions that remain behind to form the posts.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A method for making a MEMS device comprising: depositing a materialover a first electrode layer; depositing a second layer over thematerial, the second layer comprising an opening formed therethrough,the opening being configured to expose the material; flowing an etchantthrough the opening; and etching the material to remove a sacrificialportion of the material to thereby form a cavity and a support structureof the MEMS device, the support structure comprising a remaining portionof the material, the etching being non-selective between the sacrificialportion and the remaining portion of the material.
 2. The method ofclaim 1 in which the MEMS device comprises an interferometric modulator.3. The method of claim 1 in which the material is selected from thegroup consisting of molybdenum and silicon.
 4. The method of claim 1 inwhich the etching of the material is selective against the second layer.5. The method of claim 1 in which the etching comprises laterallyrecessing the material away from the opening.
 6. The method of claim 1in which the etching is isotropic etching.
 7. The method of claim 1 inwhich the etchant comprises XeF₂.
 8. The method of claim 1 furthercomprising etching the second layer to form the opening.
 9. The methodof claim 1 in which the first electrode layer comprises a first mirror.10. The method of claim 9 in which the second layer comprises a secondelectrode.
 11. The method of claim 10 in which the second layer furthercomprises a second mirror.
 12. The method of claim 1 in which the secondlayer comprises a mechanical layer.
 13. The method of claim 12 furthercomprising depositing a mirror layer, at least a portion of which issuspended from the mechanical layer after etching to remove thesacrificial portion of the material.
 14. The method of claim 13 in whichthe etching to remove the sacrificial portion is selective against themirror layer.
 15. The method of claim 13 in which the support structurehas a re-entrant profile.
 16. An unreleased MEMS substrate comprising anunderlying material and an overlying layer, the overlying layer beingconfigured so that a sacrificial portion of the underlying material isremovable to form a cavity; and the overlying layer being furtherconfigured so that a remaining portion of the underlying material formsa post structure of an interferometric modulator upon removal of thesacrificial portion, the remaining portion and the sacrificial portionhaving substantially uniform properties.
 17. The unreleased MEMSsubstrate of claim 16 in which the material is selected from the groupconsisting of molybdenum and silicon.
 18. The unreleased MEMS substrateof claim 16 in which the overlying layer comprises an apertureconfigured to expose the underlying material.
 19. The unreleased MEMSsubstrate of claim 16 in which the overlying layer comprises a pluralityof apertures configured in an array.
 20. The unreleased MEMS substrateof claim 19 in which the apertures are selected from the groupconsisting of vias, trenches and channels.
 21. The unreleased MEMSsubstrate of claim 16 in which the underlying material overlies asubstrate, the substrate comprising an aperture configured to expose theunderlying material.
 22. The unreleased MEMS substrate of claim 16 inwhich the overlying layer comprises a mirror layer.
 23. The unreleasedMEMS substrate of claim 16 in which the overlying layer comprises anelectrode.
 24. The unreleased MEMS substrate of claim 16 in which theoverlying layer comprises a mechanical layer.
 25. The unreleased MEMSsubstrate of claim 16 further comprising a first mirror layer and asecond mirror layer, at least a portion of the material being positionedbetween the first mirror layer and the second mirror layer.
 26. Theunreleased MEMS substrate of claim 25 in which the overlying layercomprises the second mirror layer.
 27. The unreleased MEMS substrate ofclaim 25 in which at least a portion of the second mirror layer issuspended from the overlying layer upon removal of the sacrificialportion.
 28. The unreleased MEMS substrate of claim 16 in which the poststructure has a re-entrant profile.
 29. A method for making aninterferometric modulator, the interferometric modulator comprising atleast a first mirror, a second mirror separated from the first mirror bya cavity, and a support structure positioned at a side of the cavity andconfigured to support the second mirror spaced from the first mirror,the method comprising: providing a substrate, the substrate having afirst area configured to underlie the first mirror and a second areaconfigured to underlie the support structure; depositing a first mirrorlayer over at least the first area; depositing a material over the firstarea and over the second area; depositing a second mirror layer over atleast the material over the first area; and forming a plurality ofopenings configured to facilitate flow of an etchant to the materialover the first area; the material over the first area being removable bythe etchant to thereby form the cavity and the support structure, wherethe support structure comprises the material over the second area, thematerial having substantially uniform properties.
 30. The method ofclaim 29 in which the material is selected from the group consisting ofmolybdenum and silicon.
 31. The method of claim 30 further comprisingremoving at least a part of the material over the first area to therebyform the cavity.
 32. The method of claim 31 wherein removing at least apart of the material over the first area to thereby form the cavitycomprises a timed etch.
 33. The method of claim 31 wherein removing atleast a part of the material over the first area to thereby form thecavity comprises laterally recessing the material away from theplurality of openings.
 34. The method of claim 32 in which the etchantcomprises XeF₂.
 35. The method of claim 29 in which the plurality ofopenings is formed through the second mirror layer.
 36. The method ofclaim 29 further comprising forming a mechanical layer over at least thematerial over the first area.
 37. The method of claim 29 in which theplurality of openings comprises a via.
 38. The method of claim 29 inwhich the plurality of openings comprises a plurality of intersectingchannels.
 39. An interferometric modulator comprising a post structure,the post structure having a re-entrant profile.
 40. The interferometricmodulator of claim 39 in which the post structure has a generallyconcave cross-section.
 41. The interferometric modulator of claim 39 inwhich the post structure has a generally convex cross-section.
 42. Themethod of claim 1 in which the etching comprises a timed etch.
 43. Themethod of claim 1 in which the support structure comprises a post.